THIS INVENTION relates to a device for generating laser radiation, and in particular to a device employing an intra-cavity optical parametric oscillator to generate the laser radiation.
An optical parametric oscillator (OPO) is a device which pumps a non-linear material with a laser to produce a coherent beam of light that can be tuned over a wide range of wavelengths, and OPO""s are useful for generating laser radiation in, for example, the mid-infrared spectral range, which radiation has many applications. Radiation in the 1 xcexcm range is suitable for pumping many types of OPO, and it has recently been proposed to pump an OPO by placing the OPO inside the resonant cavity of a Q-switched 1 xcexcm Nd:YAG laser.
However, a difficulty that is encountered when attempting to generate pumping radiation above around 10 W using such a configuration is the presence of a thermally-induced birefringence effect in the Nd:YAG laser, which hampers the generation of high-power polarised pumping radiation within the resonant cavity of the pumping laser. Thermal birefringence occurs when anisotropic thermal stress in a laser sample causes a de-polarisation of an input polarised beam, resulting in a loss in output power and a reduction in output beam quality. Optical compensation for these thermal birefringence effects is conventionally a difficult task, requiring the provision of a complex cavity with several intra-cavity optical elements. Clearly, such an arrangement is disadvantageous because of the high cost and additional time and care required to construct the complex cavity, and the provision of a large number of optical elements increases the possibility that one or more of the elements will fail or become mis-aligned.
It is an object of the present invention to seek to provide a laser radiation generation device that alleviates some of the above problems.
Accordingly, one aspect of the present invention provides an apparatus for generating laser radiation, the apparatus comprising: a pumping device comprising a resonant cavity; and a laser radiation generation element that is substantially Poynting vector walk-off compensated, the laser radiation generation element being located within the resonant cavity.
Advantageously, the pumping device is operable to produce substantially linearly polarised pumping radiation.
Preferably, standing waves within the resonant cavity converted by the laser radiation generation element to generate laser radiation having a different wavelength to that of the standing waves.
Conveniently, the pumping device further comprises a sample of laser material.
Advantageously, the laser material is a naturally birefringent laser material.
Preferably, the laser material is substantially Nd:YALO, Nd:YVO4 or Nd:YLF.
Conveniently, the laser material is substantially optically isotropic.
Advantageously, the laser material is substantially Nd:YAG.
Preferably, the apparatus further comprises a source of pumping radiation to pump the laser material.
Conveniently, the source of pumping radiation comprises at least one array of diodes.
Advantageously, the source of pumping radiation comprises at least one lamp.
Preferably, the resonant cavity is defined by a first pair of elements which are substantially reflective to radiation produced by the pumping device.
Conveniently, the laser radiation generation element comprises an optical parametric oscillator
Advantageously, the optical parametric oscillator is a xcex2-BaB2O4, LiB3O5, KTiOPO4 or LiNbO3 optical parametric oscillator.
Preferably, the laser generation element comprises a second harmonic generation device.
Conveniently, the laser radiation generation element is a non-critical phase-matched KTiOPO4, KTiOAsO4 or RbTiOAsO4 device.
Advantageously, the laser radiation generation element is provided between a second pair of reflective elements which are substantially reflective to laser radiation generated by the laser radiation generation element.
Preferably, an internal further laser radiation generation element is provided within the second pair of reflective elements.
Conveniently, the laser radiation generation element comprises a pair of crystals.
Advantageously, the crystals are bonded to one another.
Preferably, the crystals are diffusion bonded to one another.
Conveniently, an external further laser radiation generation element is provided outside the resonant cavity of the pumping device.
Advantageously, the pumping device comprises a Q-switching element.
Another aspect of the present invention provides an apparatus for generating laser radiation, the apparatus comprising: a pumping device comprising a Nd:YALO laser having a resonant cavity; and an optical parametric oscillator that is substantially Poynting vector walk-off compensated, the optical parametric oscillator being located within the resonant cavity.
A further aspect of the present invention provides an apparatus for generating laser radiation, the apparatus comprising: a pumping device comprising a resonant cavity and being operable to produce substantially linearly polarised radiation within the resonant cavity; and a laser radiation generation element that is substantially Poynting vector walk-off compensated, the laser radiation generation element being located within the resonant cavity.